The first step to installing a garden roof is to make sure that the roof structure is designed to accommodate the extra weight of the soil, plants, sod, and water necessary to successfully establish the landscaping you have designed for your roof. Our structural engineer designed a roof system taking these considerations into account, and our truss manufacturer produced trusses based on this design. Then we installed a TPO roof, an ethylene propylene rubber product that combines the durability of rubber with the proven performance of hot-air weldable seams. The roof is pitched to facilitate drainage, and has scuppers, or thru wall drains, to allow excess water or rain to drain to the ground below. The entire garden then sits on top of a layered drainage mat system that incorporates a protective fabric over the roof, a root barrier to keep plant roots from penetrating the roof, a drainage mat that allows water to find its way through the system, and a filter fabric that retains the soil while allowing the water to enter into the drainage mat. The drainage mat and filter fabric are both extended over the scuppers to retain the soil and filter the runoff.
A light weight soil medium is installed to a minimum of 4" to give sod and plants a base for growth and to help retain moisture. We are using a lightweight landscaping mix for the top 2-4" to facilitate plant and sod growth. We are installing a rock walk, planter boxes for larger plants, an herb garden, ground cover, and sod. We have installed an irrigation system to help get the garden established, and have a rain barrel to harvest rainwater to help with future irrigation needs.
Herbs in the garden will include rosemary, thyme, oregano, basil, sage, and parsley. Plants will include ice plant, aloe vera, autumn joy, bicolor iris, santolina, upright juniper, bamboo muhly, and dwarf oleander, with Zoysia grass as the sod. I have included a link to our roof garden component manufacturer's Frequently Asked Questions page for more information.